Air seeders typically comprise two or more product tanks, for carrying granular agricultural products such as seed and fertilizer, mounted on a wheeled frame assembly. A fan creates an air stream to distribute the agricultural products to furrow openers and into the soil. Modern air seeders are known that simultaneously place seed and fertilizer in the soil of a field without tillage such that a field can be seeded and fertilized in a single pass.
It is generally accepted certain types of fertilizer can be mixed with seed and placed in the same furrow, but for the higher rates and fertilizer types commonly used, it is required to provide some separation between the seed and fertilizer. Fertilizer that is placed too near the seed can damage the seed and reduce crop yield and quality, particularly with more sensitive seeds, in particular soil types and in dry soil conditions.
Common air seeder equipment is designed to place the seed and the fertilizer in different locations within essentially the same furrow, or in separate furrows that are not much more than one inch apart. A furrow opener apparatus can be mounted on the bottom end of a single shank to deliver seed and fertilizer into separate furrows, as is disclosed for example in U.S. Pat. No. 6,640,731 to Rowlett et al., and U.S. Pat. No. 6,457,426 to Cruson. Alternatively, a fertilizer furrow opener can be mounted on the bottom of one shank, with a seed furrow opener mounted at the bottom of a separate shank that is operated in close lateral proximity as disclosed for example in U.S. Pat. Nos. 5,396,851 and 5,331,907 to Beaujot, and U.S. Pat. No. 6,142,085 to Drever et al. The seeders of Beaujot and Drever include a trailing arm with separate shanks for the seed and fertilizer furrow openers extending down from the arm. A wheel on the rear end of the trailing arm packs the furrow and controls the depth of the fertilizer and seed furrow openers.
A problem with these types of systems is that in certain soil & moisture conditions, for example drier clay soils that tend to lump, it is very difficult to achieve separation of seed and fertilizer when the seed and fertilizer rows are in such close proximity. Often, some of the seed falls into the fertilizer furrow where same can be damaged. To avoid this problem, air seeders have been developed that place the fertilizer furrow about midway between the seed furrows, instead of closely adjacent to each seed furrow. An entirely separate furrow opener assembly including a shank, trip mechanism etc. is used for each seed furrow opener and for each fertilizer furrow opener. The furrow opener assemblies are spaced laterally along the frame at a desired spacing, and seed and fertilizer are directed into appropriate ones of the furrow opener assemblies to achieve the desired spacing and orientation of the seed and fertilizer in the soil.
Such an air seeder is disclosed for example in U.S. Pat. No. 6,216,616 to Bourgault. The Bourgault apparatus uses coulter disc type fertilizer furrow opener assemblies that create furrows mid way between adjacent pairs of furrows opened by coulter disc type seed furrow opener assemblies. The disclosed apparatus uses the same type of furrow opener assemblies for depositing both seed and fertilizer and does not allow independent adjustment of the seed placement openers nor does it allow independent depth control of each seed assembly during operation.